MPG Never ending question

BONOMAN5064 · May 26, 2014

Hello: So Ive had my 2014 TDI wagen for 2 months. I do most of driving on the highway. Question is I usually drive at around 80mph... The best range ive been able to get has been 470 miles on one tank. Is that normal or should i get more. Ive been doing lots of research the combined 35 mpg seems to be what i am getting. What gives? Any ideas or recommendations? Thanks.

Tuco · May 26, 2014

BONOMAN5064 said:
Hello: So Ive had my 2014 TDI wagen for 2 months. I do most of driving on the highway. Question is I usually drive at around 80mph... The best range ive been able to get has been 470 miles on one tank. Is that normal or should i get more. Ive been doing lots of research the combined 35 mpg seems to be what i am getting. What gives? Any ideas or recommendations? Thanks.

That's easy, slow down. There is @ a 33% increase in aerodynamic drag at 75 mph vs 65 mph. It's probably closer to a 40% increase at 80 mph. The JSW seems to have a higher coefficient of drag than the Jetta and Golf, so fuel economy will be worse no matter what.

Scoutx · May 26, 2014

2014 Jetta Wagon - Drag coefficient = 0.31

2014 Jetta - Drag coefficient = 0.30

2014 Golf - Drag coefficient = 0.32

Lower is better

Yes, 80 is hard on your fuel economy, also after only 2 months you are still in the break-in period. So mileage is going to be less. It will slowly climb until about 8-10K.
Also how you drive at 80 can have a big impact as well as how you drive before and after you hit the interstate.

Lincoln · May 27, 2014

Lots of threads about improving mileage. Biggest impact for you would be to slow down. If that's not an option, then the next biggest impact will come from looking far ahead at traffic to avoid braking/acceleration cycles. Pulse and glide may help some too, but will have much lower impact at 80mph than at 60mph due to much shorter glide periods. Most of us get better with time too just by paying attention to mileage and learning as we go.

oilhammer · May 27, 2014

I have to ask: what other new car could you drive at 80 that could get 35 MPG? I'd bet not many. I'd not slow down, either. I'd keep enjoying my new car!

The older ones can get better, but they are not as fast nor as "clean".

sdgt3 · May 27, 2014

I wondered why the Passat, a bigger, heavier, and wider car than the JSW was rated at a higher EPA mileage figure and simply chalked it up to something about the design allowed it to be more aero efficient despite its size. Sure enough, the drag coefficient of the current model year Passat is .029.

Driving the Passat at 80 mph vs 75 mph netting me 4 more mpg over a 200 mile distance on the highway

oilhammer · May 27, 2014

The Passat has SCR, and a different engine, than the Golf-Jetta-Beetle.

nkgagne · May 27, 2014

I read that drag increases at the square of velocity, so if you want better fuel economy, speed is your enemy. Slow down to 70 for a tank and notice the improvement. Depending on your commute, it shouldn't make a huge difference. If you'd rather just get there quick and don't really care about the FE penalty, well, then keep doing what you're doing.

sdgt3 · May 27, 2014

oilhammer said:
The Passat has SCR, and a different engine, than the Golf-Jetta-Beetle.

I thought the current models of Jetta, JSW and Passat had the same 2.0 tdi engine? Scr?

oilhammer · May 27, 2014

sdgt3 said:
I thought the current models of Jetta, JSW and Passat had the same 2.0 tdi engine? Scr?

They don't.

2009 Golf, Jetta, JSW, and all Audi A3s use the CBEA engine.

2010+ Golf, Jetta, JSW, and Beetle use the CJAA.

2012+ Passat uses the CKRA.

SCR = Selective Catalyst Reduction, and is a NOx mitigation system that works post-combustion, which allows a diesel to do what a diesel does best: run lean(er). This means less fuel used, less PM produced, less DPF regens.

The CKRA uses almost all different parts than the CBEA/CJAA engines. The entire fuel system, EGR system, exhaust system, timing system, cooling system, charge air system, etc. is different.

IndigoBlueWagon · May 27, 2014

Given you're in FL I assume you're also running the A/C. 35 seems a bit low, but not terrible. I've seen mid-40s running at 75-85 with the A/C on in my Golf.

If you use cruise control a lot, try a tank without it. I bet you'll pick up a few MPG. And the car will improve with more break-in.

BONOMAN5064 · May 27, 2014

I figured that 80 might be a bit much. Then again here in South Florida turnpike and I 75 min speed is 70. Yes I do use my AC and no.. Do not use my cruise control much. I drive 70 miles a day 5 days a week. Thats about 350 miles per week. I read the threads for break in: moderate speed...watch revs .... Also follow the cold start procedures thread... I have tried to educate myself since this is my first diesel. I am really enjoying it. Love how she cruises on the highway...love the sunroof... And love the efficiency.. I had a mustang gt before..lol

IndigoBlueWagon · May 27, 2014

I'd say don't worry about the FE and enjoy the car. As oilhammer wrote, what other car can get 35 MPG at 80? These cars are a pleasure at higher speeds.

sdgt3 · May 27, 2014

oilhammer said:
They don't.

2009 Golf, Jetta, JSW, and all Audi A3s use the CBEA engine.

2010+ Golf, Jetta, JSW, and Beetle use the CJAA.

2012+ Passat uses the CKRA.

SCR = Selective Catalyst Reduction, and is a NOx mitigation system that works post-combustion, which allows a diesel to do what a diesel does best: run lean(er). This means less fuel used, less PM produced, less DPF regens.

The CKRA uses almost all different parts than the CBEA/CJAA engines. The entire fuel system, EGR system, exhaust system, timing system, cooling system, charge air system, etc. is different.

Thanks for the education. Not to get off topic too much but why would VAG use a different system on the Passat than it's other models since it would cost less if out of the same parts bin?

BoB JSDubb · May 27, 2014

BONOMAN5064 said:
I figured that 80 might be a bit much. Then again here in South Florida turnpike and I 75 min speed is 70. Yes I do use my AC and no.. Do not use my cruise control much. I drive 70 miles a day 5 days a week. Thats about 350 miles per week. I read the threads for break in: moderate speed...watch revs .... Also follow the cold start procedures thread... I have tried to educate myself since this is my first diesel. I am really enjoying it. Love how she cruises on the highway...love the sunroof... And love the efficiency.. I had a mustang gt before..lol

Try using the real time mpg gauge. It helps see the real time data of different throttle positions. As you learn when to glide, avoid braking and accelerate properly, it will increase.

Tuco · May 27, 2014

BoB JSDubb said:
Try using the real time mpg gauge. It helps see the real time data of different throttle positions. As you learn when to glide, avoid braking and accelerate properly, it will increase.

^^^ very true.

If you want to maximize fuel economy, set your cruise control to 70 and stay in the right lane. If you're lucky, you can find someone else driving @ 70 using their cruise control, and stay @ 2.5 to 3 car lengths behind them. 70 mph will add less than 8 minutes to your daily commute, and will have 31% less aerodynamic drag than 80 mph. This should get you in the low to mid 40's.

SkeeterMark · May 28, 2014

Check your average speed at the end of a tank. This will help determine how much of the time you're actually driving 80 vs. the piddly driving you likely have at the start and end of your commute. This might help you to determine where you're losing the mileage. I drive 130 miles per day round trip, 100 of it on freeway at 75-80mph, yet my average speed on a tank is usually around 50mph. As you can see, I am over 45 mpg lifetime, so the 80 mph is not exactly killing the FE (though it would certainly be better if I drove slower). Most of my mileage hit comes in the off-freeway driving, and it increases during the freeway stage, of which I have more than you.

And as mentioned, if you're using your AC a lot, that will bring you down around 5% right there.

kjclow · May 28, 2014

Just passed 65K miles in my 2010 JSW and lifetime average is pushing just over 40 mpg. Most of my driving is a short commute of less than 10 miles with varied traffic. This morning, I don't think I got over 35 mph. I can often make the trip with an average speed around 45, including two lights and one stop sign.

Anyway, I've done a couple of long distance cruises in the past couple of months. A run to Atlanta and a run to Hilton Head, both 4+ hours of driving. What I noticed is that the MFD on my cars says I get better mileage in the 70-75 range than the 65-70 range. MFD shows a 2-3 mpg difference at those speeds. Atlanta round trip averaged 45, and the Hilton Head round trip averaged 44. The difference in the trips was probably due to the construction on I-26 east of Columbia.

hybridkiller · Jun 1, 2014

kjclow said:
What I noticed is that the MFD on my cars says I get better mileage in the 70-75 range than the 65-70 range.

You gotta factor wind speed/direction into it. It is likely that a tailwind or headwind (or both) skewed your results. Either that or you've somehow managed to defy the laws of physics.

I prefer to calculate my highway consumption over several thousand miles before I try to draw any broad conclusions about my average MPG.

eddjmemg · Jun 1, 2014

I also drive fast on the highway. When the car is new you will not get the best mpg. You'll get the EPA advertised sure but this is a diesel you'll get better in time. My mpg kept getting better even after 20k miles. You'll really learn how to drive it later. DO use cruise control. It works! My wife now gets better mpg just because she started using it. Let's be realistic, you're not gonna slow down. I say get a good radar detector and use cruise control and in time that engine will break in n get you into the 40s+. Just be patient.

kjclow · Jun 2, 2014

hybridkiller said:
You gotta factor wind speed/direction into it. It is likely that a tailwind or headwind (or both) skewed your results. Either that or you've somehow managed to defy the laws of physics.

What I noticed is that on the same direction portion of a trip, so removing the wind factor, is that if I leave the cruise set at about 68, the mpg on the mfd will get to a certain peak (around 42 )and then start slowly dropping. On the other hand, if I set the cruise at 72, than the MFD will continue climbing towards 45+. I've got a run to chapel Hill this week, I'll see if I can snap a few pictures of it.

hybridkiller · Jun 2, 2014

No need for pictures, I wasn't disputing what you are seeing - I just don't think you can draw any broad conclusions from it - especially when it goes against laws of aerodynamics. Even assuming the wind always came from precisely the same direction (which it doesn't) wind speed is by no means a constant either. You might have (relative) calm on one occasion, 5 mph tailwind on another, 10 mph tailwind on yet another - all same direction.

kjclow · Jun 2, 2014

I know. Just an observation over the past month because I had nothing else to entertain me on those long trips. I don't see how anyone can stand those hour plus commutes. I would go insane.

hybridkiller · Jun 2, 2014

I regularly go back and forth between FL and NE GA, and monitoring my mpg has long been a form of entertainment for me too. Listening to music/news/Howard Stern gets old after a couple of hours.

kjclow · Jun 2, 2014

For me, listening to Howard Stern gets old after about 5 minutes.

gloaming · Jun 2, 2014

eddjmemg said:
DO use cruise control. It works!

I wouldn't entirely agree with that. Cruise control works if you haven't gotten down the hypermiling techniques, but once you learn the tricks CC usually gets me 5mpg less then just using my right foot. I like to lock my foot in place when going up a hill and stay at a constant rpm and maintain a constant boost rather than a constant speed. maybe the occasional person has to pass me in the left lane but I'm still getting 50+mpg realtime going up steep hills

kjclow · Jun 2, 2014

What I notice with cruise is more engine braking than I would use manually. Look at your instant mileage and you'll see when cruise kicks in the engine to slow down after cresting a hill. If I were hypermiling, I would let the car coast in gear longer.

hybridkiller · Jun 2, 2014

There's definitely a consumption penalty when the CC is forcing the engine to maintain a set speed while climbing a hill - I think that's the biggest disadvantage to using it.
That said, I do 10+ hour drives on a regular basis, so frequent use of CC is a luxury I won't give up - although I do toggle it on and off in order to take advantage of steep hills etc.
That said, if I keep it under 65mph, and assuming no headwind, judicious use of CC still routinely gets me north of 50 mpg.

eddjmemg · Jun 2, 2014

He drives 80 mph. So any hypermiling is prob not even considered. You're not hypermiling at that speed. No one is passing you. You're not pissing people off for going too slow. We can come up with our own ideas on how to gain your best mileage but if I reread what the OP asked n said I look at myself and I do the same thing. I've done the hypermiling sure it's great but I'd rather do 80 mph getting "only" 40-45 mpg. Cc works great at those speeds.

oilhammer · Jun 2, 2014

I find it somewhat humorous that so many people worry so much about fuel economy with a TDI. To me, that is the best part of owning them: you DON'T have to worry. Because no matter how you drive them, so long as they are in good working order, your fuel economy will always be very good.

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